TEM Study of the Formation and Modification of Nanocrystalline Si Inclusions in a-Si:H Films

Abstract

Transmission electron microscopy has been used to investigate the formation and modification of the nanocrystalline silicon ( nc -Si) phase in thin a -Si:H films. The films were produced by three different methods: plasmochemical deposition of a-Si:H, cyclic plasmochemical deposition with intermediate annealing of layers 10-20 nm in thickness in hydrogen plasma, and plasmochemical deposition of a -Si:H with the annealing of 40-nm-thick films in hydrogen plasma. In the films produced by cyclic deposition with intermediate annealing in hydrogen plasma and subsequent thermal treatment at 750 ° C for 30 min, the size of nanocrystallites does not exceed the thickness of a layer deposited in a cycle. In contrast, in uniform films with similar thermal treatment, crystallites may be as large as 1 µ m or more. Models that account for the effects observed are suggested. These models are validated by calculating profiles of hydrogen diffusion in a -Si:H film after annealing in hydrogen plasma and thermal treatment in vacuum. © 2004 MAIK "Nauka/Interperiodica". nmFig. 1. Cross-sectional TEM image of a -Si:H film produced by cyclic deposition.

Morphology and optical properties of α-Si:Y films obtained by the electron-beam evaporation method

“…These images are very close to the results of electron microscopy of amorphous α-Si:Н films with small number of nanocrystalline inclusions that were prepared by the chemical vapor deposition method [7]. Both in the work [7] and in presented images, one can see dark points. These points can be interpreted as the film defects or graphite inclusions.…”

“…First variant is that yttrium creates the impurities levels increasing photosensitivity. Next reason is that nanocrystalline inclusions remove in part the mechanical stresses in amorphous matrix [7]. Thus, the less strained amorphous network with a lower concentration of weak bonds is formed.…”

“…However, in practice the α-Si〈nc-Si〉 film photoconductivity is higher by an order of magnitude than that of amorphous silicon films [6]. There is no commonly adopted explanation of this fact [6,7].…”